102 NORMAL HISTOLOGY. 



processes is an axis-cylinder process. The multipolar cells have 

 one axis-cylinder process, the rest being of the dendritic type 

 already mentioned, which are distinguished as "protoplasmic" 

 processes. 



Nerve-cells are, as a rule, larger than the other cytoplasmic cells 

 of the body, with the exception of the larger epithelial cells. Their 

 cytoplasm is so finely granular that the cells look much more trans- 

 parent than those of epithelium. With a high power the cytoplasm 

 frequently exhibits fine striations, which are prolonged into the 

 processes, giving them an appearance of longitudinal fibrillation. 

 These appearances are due to the arrangement of the fibrils of 

 spongioplasm. Considerable attention has of late been given to 

 certain granules, which become evident in the cytoplasm when 

 nerve-cells have been fixed in alcohol or in acid solutions. These 

 granules have an affinity for dyes, " chromophilic granules," and 

 usually occur in groups in the neighborhood of the nucleus. Their 

 significance is not yet understood. 



The protoplasmic processes of the nerve-cells diminish in diam- 

 eter as they branch, and they also present occasional varicosities, 

 which give them an irregular contour. They terminate either in 

 fine-pointed extremities or in little, knobbed ends, and do not unite 

 with those of neighboring cells, but form with them an intricate 

 interlacement of delicate nervous twigs. 



The axis-cylinder processes arise in conical extensions of the cell, 

 and then become uniform in diameter and of a smooth contour 

 without varicosities. When they branch the two divisions retain 

 their size throughout their course until they enter into the forma- 

 tion of some terminal structure. 



The average size of the nuclei of nerve-cells is greater than that 

 of the other nuclei in the body, but they appear to contain less 

 chromatin, and therefore stain less deeply and present a less distinct 

 intranuclear reticulum. 



Nerve- or ganglion-cells are found in the gray matter of the 

 (•■iitral nervous system, in the ganglia, and sometimes in the course 

 of nerves and in their peripheral terminations (Fig. 88). 



2. Nerve-fibres. — There are two varieties of nerve-fibres : the 

 white, or medullated, and the gray, or non-medullated. These 

 differ both in their appearance when seen by the unaided eye and 

 in their microscopical structure. 



(a) Medullated nerve-fibres eonsist of a central cylindrical struct- 



